The Total Trypsin Inhibitory Capacity of the pancreas of 14 inbred strains of rats of both sexes has been determined. Three strains were found to possess a "low" inhibitory capacity, and 2 strains a "high" inhibitory capacity. It is planned now to use rats of these strains to test the hypothesis that there is a link between content of proteinase inhibitors in the pancreas, and the type and severity of the pathology that can be elicited in the pancreas by various experimental manipulations of the animals. Work is also in progress aimed at the isolation, separation and characterization of rat pancreas proteinase inhibitors, with the long-term goal of determining whether the content of proteinase inhibitors in mammalian pancreas is under genetic control.